Unlike conventional viral nucleic acids […] none of these RNAs code for specific coat proteins that are capable of self-assembly into capsids. These entities, therefore, exist only in the vegetative phase; the dormant phase so characteristic of viruses (i.e., the virion) is absent. I propose the term ‘viroid’ for such entities. Altenburg (1946) introduced this term to designate hypothetical symbionts, akin to viruses […]. If, however, the ‘viroid’ is redefined operationally and in modern terms to encompass nucleic acid species with the properties discussed here, the term serves a useful function.